Re: [Bitcoin-development] New BIP32 structure

[Allen Piscitello <allen.piscitello@gmail.com>]

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For every branch (say multiple accounts), how would a new wallet be able to
know how many sequence items to scan?  It seems like not only do you need
to have standard rules for the hierarchy, but how the usage can be
detected.  The other scanning seems pretty straightforward.  For accounts,
it seems like you could have a situation where you want to initially set up
10 different accounts, but only account #10 gets any transactions.  If a
new wallet was trying to scan with this seed, it would have to know to keep
scanning each account until it found the account.  The user would have to
be responsible for knowing how many accounts there are, or some rules would
need to be in place to not allow creating accounts until earlier accounts
can be proven to have existed in the blockchain.  Or I am missing something.

-Allen

On Wed, Mar 26, 2014 at 3:49 PM, Mike Hearn <mike@plan99.net> wrote:

> Myself, Thomas V (Electrum) and Marek (Trezor) got together to make sure
> our BIP32 wallet structures would be compatible - and I discovered that
> only I was planning to use the default structure.
>
> Because I'm hopeful that we can get a lot of interoperability between
> wallets with regards to importing 12-words paper wallets, we brainstormed
> to find a structure acceptable to everyone and ended up with:
>
>   /m/cointype/reserved'/account'/change/n
>
> The extra levels require some explanation:
>
>    - cointype:  This is zero for Bitcoin. This is here to support two
>    things, one is supporting alt coins based off the same root seed. Right now
>    nobody seemed very bothered about alt coins but sometimes feature requests
>    do come in for this. Arguably there is no need and alt coins could just use
>    the same keys as Bitcoin, but it may help avoid confusion if they don't.
>
>    More usefully, cointype can distinguish between keys intended for
>    things like multisig outputs, e.g. for watchdog services. This means if
>    your wallet does not know about the extra protocol layers involved in this,
>    it can still import the "raw" money and it will just ignore/not see the
>    keys used in more complex transactions.
>
>    - reserved is for "other stuff". I actually don't recall why we ended
>    up with this. It may have been intended to split out multisig outputs etc
>    from cointype. Marek, Thomas?
>
>    - account is for keeping essentially wallets-within-a-wallet to avoid
>    mixing of coins. If you want that.
>
>    - change is 0 for receiving addresses, 1 for change addresses.
>
>    - n is the actual key index
>
> For bitcoinj we're targeting a deliberately limited feature set for hdw v1
> so I would just set the first three values all to zero and that is a
> perfectly fine way to be compatible.
>
> The goal here is that the same seed can be written down once, and meet all
> the users needs, whilst still allowing some drift between what wallets
> support.
>
> Pieter made the I think valid point that you can't really encode how keys
> are meant to be used into just an HDW hierarchy and normally you'd need
> some metadata as well. However, I feel interop between wallets is more
> important than arriving at the most perfect possible arrangement, which
> feels a little like bikeshedding, so I'm happy to just go with the flow on
> this one.
>
>
>
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